Cooling system

ABSTRACT

A cooling system comprises a first heat exchanger installed inside a room; a second heat exchanger installed outside the room; and a piping system that enables a refrigerant to naturally circulate between the first heat exchanger and the second heat exchanger. The piping system includes the first supply pipe and the second supply pipe. The first supply pipe supplies liquid refrigerant from the second heat exchanger to the first heat exchanger and the liquid refrigerant is heated by heat exchanging in a third heat exchanger with vaporized refrigerant supplied from the first heat exchanger to the second heat exchanger. The second supply pipe supplies liquid refrigerant from the second heat exchanger to the first heat exchanger bypassing the third heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-100810, filed Apr. 26, 2010, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a natural circulation (vapor-phase circulation)-type cooling system that cools a room by enabling refrigerant to naturally circulate between a first heat exchanger installed in a room and a second heat exchanger installed outside the room.

BACKGROUND

Japanese Laid-Open Patent Publication No. 2003-347782 discloses a cooling apparatus that is capable of further suppressing condensation on the surfaces of a heat exchanger provided in a room. To do so, an ebullient cooling apparatus that cools the interior of a case according to Publication No. 2003-347782 includes a control device that stops a fan outside the room and continuously drives a fan inside the room when a condensation environment has been detected according to signals from a temperature sensor that detects the temperature of the surface of the heat exchanger inside the room and a humidity sensor that is disposed next to the temperature sensor and detects the humidity. By doing so, when the surfaces of the heat exchanger in the room have become a condensation environment, the temperature of such heat exchanger can be set equal to the room air temperature in a short time, reliably suppressing the occurrence of condensation. Note that hereinafter, the term “interior” refers to inside a room subject to cooling and the term “exterior” refers to outside such room. The terms “indoor” and “outdoor” refer to inside and outside a building.

SUMMARY

A natural circulation-type (vapor-phase circulation) cooling system that does not include a compressor and cools a room by enabling refrigerant to naturally circulate between a first heat exchanger installed inside a room (indoors) and a second heat exchanger installed usually outside the room (and in particular, outdoors) is known. Such natural circulation-type cooling system is advantageous in that it is possible to cool a room with little power consumption when the temperature of outside the room is lower than that of inside the room. For a natural circulation-type cooling system, it is important to suppress condensation on the heat exchanger unit installed in the room.

With the technology disclosed in Publication No. 2003-347782 mentioned above, if the environment of the surface of the interior heat exchanger is in a condensation condition even when the outdoor fan is stopped, circulation of the refrigerant is stopped to prevent condensation. This means that the above advantage of a natural circulation-type (vapor-phase circulation) cooling system is not fully realized.

One aspect of the present invention is a cooling system including: a first heat exchanger installed inside a room; a second heat exchanger installed outside the room; and a piping system that enables a refrigerant to naturally circulate between the first heat exchanger and the second heat exchanger. The piping system includes the first supply pipe and the second supply pipe. The first supply pipe supplies liquid refrigerant from the second heat exchanger to the first heat exchanger and the liquid refrigerant is heated by heat exchanging in a third heat exchanger with vaporized refrigerant supplied from the first heat exchanger to the second heat exchanger. The second supply pipe supplies liquid refrigerant from the second heat exchanger to the first heat exchanger bypassing the third heat exchanger.

In this cooling system, the first supply pipe supplies heated liquid refrigerant, which has been heated with the vaporized refrigerant in the third heat exchanger, to the first heat exchanger. Accordingly, even if the temperature of the refrigerant outputted from (output of) the second heat exchanger is a temperature at which condensation occurs at the first heat exchanger unit or lower, by heating the liquid refrigerant using the third heat exchanger, it is possible to suppress condensation at the first heat exchanger.

In addition, since it is possible to cause the refrigerant to circulate naturally via the first supply pipe even when the temperature of the liquid refrigerant supplied from the second heat exchanger is a temperature at which condensation occurs at the first heat exchanger or lower, it is possible to maintain the amount (circulated amount) of refrigerant supplied to the second heat exchanger. This means that even when the temperature of the liquid refrigerant supplied from the second heat exchanger is a temperature at which condensation occurs at the first heat exchanger or lower, it is still possible to cool the room using the cooling system. Therefore, according to this natural circulation (vapor-phase circulation)-type cooling system, it is possible to cool a room with low power consumption or without power consumption while suppressing condensation at the first heat exchanger unit even in conditions where the outside air temperature is even lower.

On the other hand, when the temperature of the liquid refrigerant supplied from the second heat exchanger has not fallen as far as a temperature where condensation occurs at the first heat exchanger, it is possible to use the second supply pipe to supply liquid refrigerant from the second heat exchanger to the first heat exchanger bypassing the third heat exchanger. Accordingly, a drop in the cooling effect can be suppressed in such cases.

It is preferable for the piping system to include a changeover valve system that switches between using the first supply pipe and the second supply pipe, for the cooling system to further comprise a control unit that controls the changeover valve system, and for the control unit to include a function (functional unit) that switches from the second supply pipe to the first supply pipe using the changeover valve system when a temperature of liquid refrigerant outputted from the second heat exchanger becomes equal to or below a first set temperature. It is possible to automatically select the first supply pipe and the second supply pipe according to the temperature of the liquid refrigerant. A typical example of the first set temperature is a temperature at which there is the risk of condensation occurring at the first heat exchanger.

One of aspects of the second heat exchanger includes a second tube and a second fan that supplies outside air to the second tube. It is possible to drive the second fan and maintain the cooling effect while suppressing condensation at the first heat exchanger even in conditions where the outside air temperature is low.

In addition, the control unit may include a function (functional unit) that stops the second fan before switching from the second supply pipe to the first supply pipe using the changeover valve system when the temperature of the liquid refrigerant outputted from the second heat exchanger becomes equal to or below the first set temperature. By stopping the second fan that consumes power before switching from the second supply pipe to the first supply pipe, it is possible to cool the room even more efficiently. The first heat exchanger includes a first tube and may include or not include a first fan that supplies room air to the first tube. By omitting the first fan, it is possible to cool the room with even lower power consumption.

The control unit may preferably include a function (functional unit) that closes the first supply pipe and the second supply pipe using the changeover valve system when the temperature of the outside air becomes equal to or below a second set temperature that is lower than the first set temperature. When the temperature of the liquid refrigerant supplied to the first heat exchanger becomes a temperature at which condensation occurs at the first heat exchanger or lower even when such liquid refrigerant is heated by the third heat exchanger, by stopping the circulation of the refrigerant, it is possible to prevent condensation at the first heat exchanger.

Another aspect of the present invention is a hybrid air conditioning system including: the cooling system described above, and a main air conditioning system that further cools air that has been cooled by the first heat exchanger of the cooling system and supplies the cooled air.

Yet another aspect of the present invention is a control method for a cooling system including a first heat exchanger installed inside a room, a second heat exchanger installed outside the room, and a piping system that enables a refrigerant to naturally circulate between the first heat exchanger and the second heat exchanger. The piping system included in the cooling system includes: a first supply pipe that supplies liquid refrigerant, which has been heated by heat exchanging in a third heat exchanger with vaporized refrigerant supplied from the first heat exchanger to the second heat exchanger, from the second heat exchanger unit to the first heat exchanger unit; a second supply pipe that supplies liquid refrigerant from the second heat exchanger to the first heat exchanger bypassing the third heat exchanger; and a changeover valve system that switches between using the first supply pipe and the second supply pipe. This control method includes a step (a step of switching) of having a control unit that controls the changeover valve system switch from the second supply pipe to the first supply pipe using the changeover valve system when a temperature of liquid refrigerant outputted from the second heat exchanger becomes equal to or below a first set temperature.

According to this control method, when the temperature of the liquid refrigerant supplied from the second heat exchanger is equal to or below a first set temperature, typically a temperature at which there is a risk of condensation occurring at the first heat exchanger, it is possible to switch the circulation path of the refrigerant from the second supply pipe to the first supply pipe to suppress condensation at the first heat exchanger.

When the second heat exchanger includes a second tube and a second fan that supplies outside air to the second tube, the control method may further comprise a step of stopping the second fan before the switching when the temperature of the liquid refrigerant outputted from the second heat exchanger becomes equal to or below the first set temperature.

Compared to switching the circulation path of the refrigerant from the second supply pipe to the first supply pipe, it is possible to further lower the power consumption by stopping the second fan, and there is also the possibility of suppressing condensation at the first heat exchanger.

The control method may preferably further include a step of closing the first supply pipe and the second supply pipe using the changeover valve system when the temperature of the outside air becomes equal to or below a second set temperature that is lower than the first set temperature.

By doing so, it is possible to stop the circulation of the refrigerant when the temperature of the liquid refrigerant supplied to the first heat exchanger has fallen to a temperature where condensation occurs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an overview of a hybrid air conditioning system including a cooling system according to an embodiment of the present invention;

FIG. 2 is a diagram schematically showing circulation of refrigerant in the cooling system;

FIG. 3 is a diagram schematically showing circulation of refrigerant by the cooling system when the outside air temperature is even lower;

FIG. 4 shows one example of an interior heat exchanger;

FIG. 5 is a flowchart of a control method for the cooling system; and

FIG. 6 shows an overview of a hybrid air conditioning system including a cooling system according to another embodiment of the present invention.

DETAIL DESCRIPTION

FIG. 1 shows one example of a cooling system of a data center. This cooling system (hybrid air-conditioning system) 10 a cools the servers 5 and the room (indoors) 1. A raised (access) floor 2 has a two-level construction composed of a floor surface 2 a and an underfloor 2 b. The cooling system 10 a supplies cooling air 61 to a plurality of servers 5 disposed on the floor surface 2 a using the space of underfloor 2 b. The hybrid air-conditioning system 10 a includes a floor-standing main air conditioning system 20 and a cooling system (supplementary air conditioning system) 11 disposed near the ceiling 3 of the room 1.

The main air conditioning system 20 includes a floor-standing indoor (interior) unit 21 and an outdoor unit 29. The indoor unit 21 includes an evaporator 24 including cooling tubes, a heater 25, and an interior fan (indoor fan) 22. The indoor unit 21 takes in air via an intake 23 a at a ceiling side of the indoor unit 21, controls the temperature of the air, and expels air (cooling air) 61 whose temperature has been controlled into the underfloor space 2 b from an outtake 23 b provided so as to pass through the floor 2. The outdoor unit 29 includes a compressor 26, an outside fan 27, and a condenser 28.

In the main air conditioning system 20, refrigerant that has been compressed by the compressor 26 is cooled by the condenser 28 using the outside air temperature, then, in the evaporator 24 of the indoor unit 21, by reducing the pressure and evaporating the refrigerant to evaporate, the cooling air 61 is generated. In the indoor unit 21, the air 65 drawn in from the intake 23 a by the interior fan 22 is cooled by the evaporator 24 and the resulting cooling air 61 is expelled to the underfloor space 2 b to cool the servers 5. At the servers 5, electronic equipment inside the servers 5 is cooled by the cooling air 61 supplied from the underfloor space 2 b and heated air 62 is discharged toward the ceiling 3.

FIGS. 2 and 3 show the cooling system 11 extracted from the hybrid air-conditioning system 10 a. FIG. 2 schematically shows circulation (cycling) of the refrigerant in a state where the outside temperature is lower than the room temperature but is not sufficiently low to cause condensation to occur in the room. FIG. 3 shows circulation (cycling) of the refrigerant in a state where the outside temperature is low and there is the possibility that condensation would occur if no countermeasures were taken.

The cooling system 11 includes a first heat exchanger (or “interior heat exchanger”, “interior heat exchanger unit”, “indoor heat exchanger unit”, or “room apparatus”) 30 that is installed in the room (indoors) and a second heat exchanger (or “exterior heat exchanger”, “exterior heat exchanger unit”, “outside heat exchanger unit”, or “outside apparatus”) that is installed outside the room, typically installed outdoor (outside). The interior heat exchanger 30 includes a plurality of interior tubes (first tubes) 31 disposed at an angle or perpendicular to (i.e., vertically) the ceiling 3 of the room 1 that extends in the horizontal direction (note that only one indoor tube is shown in the drawings), a supply header 32 that is supplied with liquefied refrigerant, and a discharge header 33 that collects vaporized refrigerant, with the plurality of interior tubes 31 being connected to both the supply header 32 and the discharge header 33. Note that the in-room heat exchanger 30 according to the present embodiment does not include a fan (interior fan).

In the interior heat exchanger 30, the discharge header 33 is disposed closer to the ceiling 3 than the supply header 32. This means that the plurality of interior tubes 31 extend diagonally or vertically upward from the supply header 32 toward the discharge header 33.

The interior heat exchanger 30 includes the interior tubes 31 that are disposed in a housing 39. In FIG. 1, in the same way as the interior tubes 31, the housing 39 is installed so as to be inclined with respect to the ceiling 3. The upper surface of the housing 39 is a supply opening 38 a through which air is supplied to the interior tubes 31, and the lower surface of the housing 39 is an outtake 38 b that discharges air that has been cooled by the interior tubes 31. The outtake 38 b is connected via a duct 37 to the intake 23 a of the floor-standing interior unit 21.

Note that although the interior heat exchanger 30 is supported via the duct 37 by the floor-standing interior unit 21 in this supplementary air conditioning system 11, it is also possible to suspend the interior heat exchanger 30 from the ceiling 3 using an appropriate method or to support the interior heat exchanger 30 from the floor 2. Also, the housing 39 may be disposed or installed so as to be perpendicular to the ceiling 3.

The exterior heat exchanger 40 is outside the room (and typically outdoors) 9 and includes a plurality of exterior tubes (second tubes) 41 installed at a higher position than the interior tubes 31, a supply header 42 that is supplied with vaporized refrigerant, and a discharge header 43 that discharges liquid refrigerant, with the plurality of exterior tubes 41 connecting the supply header 42 and the discharge header 43. In this exterior heat exchanger 40 the supply header 42 supplied with the vaporized refrigerant is disposed so as to be positioned higher than the discharge header 43 that discharges liquid refrigerant and the exterior tubes 41 are disposed in the perpendicular direction so as to join the supply header 42 and the discharge header 43. The exterior heat exchanger 40 further includes an exterior fan (second fan) F2 that forcibly supplies outside air 8 to the exterior tubes 41 and a fan motor 45 that drives the exterior fan F2. In this exterior heat exchanger 40, the exterior fan F2 suctions the air for supplying the air to the exterior tubes 41.

Typical examples of the interior tubes 31 and the exterior tubes 41 are aluminum tubes or copper tubes, and such tubes may be equipped with fins or may be finless. When fins are used, such fins may be corrugated, plate-like, or in the form of spines. The refrigerant may be any refrigerant that vaporizes at room temperature and liquefies at outside air temperature as operating conditions, and as one example, HFC134a (whose chemical formula is CH₂FCF₃) may be used.

The cooling system 11 further includes a piping system 70 that enables the refrigerant to naturally circulate between the interior heat exchanger 30 and the exterior heat exchanger 40. The piping system 70 of the cooling system 11 connects (fluidly connects) the interior tubes 31 of the interior heat exchanger 30 and the exterior tubes 41 of the exterior heat exchanger 40 with no compressor in between.

The piping system 70 includes pipes (or “connecting pipes” or “supply pipes”) 71 to 75 and a changeover valve system 76. The first supply pipe 71 is a pipe for liquid refrigerant and connects (fluidly connects) an outlet pipe 73 of the exterior heat exchanger 40 and an inlet pipe 74 of the interior heat exchanger 30. From the exterior heat exchanger 40-side, a first valve CV1 and an internal heat exchanger (or “third heat exchanger”) 90 are provided on the first supply pipe 71. A pipe (vaporized refrigerant supply pipe) 75 for vaporized refrigerant (i.e., refrigerant that has boiled and vaporized in the interior tubes 31) that supplies vaporized refrigerant from the interior heat exchanger 30 to the exterior heat exchanger 40 is connected (fluidly connected) to the internal heat exchanger 90 so as to the vaporized refrigerant pass thought the internal heat exchanger 90, with the liquid refrigerant supplied by the first supply pipe 71 being heated inside the internal heat exchanger 90 and supplied to the interior heat exchanger 30. Accordingly when the first valve CV1 is opened, liquid refrigerant that has been heated by vaporized refrigerant in the internal heat exchanger 90 can be supplied via the first supply pipe 71 to the interior heat exchanger 30. That is, the first supply pipe 71 is a pipe for supplying liquid refrigerant, which has been heated by heat exchange with vaporized refrigerant supplied from the interior heat exchanger 30 to the exterior heat exchanger 40 in the internal heat exchanger 90, from the exterior heat exchanger 40 to the interior heat exchanger 30.

The second supply pipe 72 is a pipe for liquid refrigerant that connects (fluidly connects) the outlet pipe 73 of the exterior heat exchanger 40 and the inlet pipe 74 of the interior heat exchanger 30. A second valve CV2 is provided on the second supply pipe 72 between the branch of the first supply pipe 71 and the interior heat exchanger 30. The second supply pipe 72 connects the outlet pipe 73 of the exterior heat exchanger 40 and the inlet pipe 74 of the interior heat exchanger so as to bypass the internal heat exchanger (the third heat exchanger) 90. Accordingly, when the second valve CV2 is opened, liquid refrigerant can be supplied to the interior heat exchanger 30 via the second supply pipe 72 so as to bypass the internal heat exchanger 90.

The third supply pipe (vaporized refrigerant supply pipe) 75 is a pipe for supplying vaporized refrigerant (i.e., refrigerant that has boiled and vaporized in the interior tubes 31) from the interior heat exchanger 30 to the exterior heat exchanger 40. The liquid refrigerant supply pipes (the first and second supply pipes) 71 and 72 and the vaporized refrigerant supply pipe 75 fluidly connect between the interior heat exchanger 30 and the exterior heat exchanger 40 disposed higher than the interior heat exchanger 30 so that fundamentally no counter gradient is produced midway in the pipes.

FIG. 4 shows one example of the internal heat exchanger (the third heat exchanger) 90. The internal heat exchanger 90 shown in FIG. 4 is a double pipe-type heat exchanger and includes an outer pipe 91 provided so as to surround the outside of the supply pipe 75 through which the vaporized refrigerant 81 flows. Heat exchanging occurs between the vaporized refrigerant 81 passing through inside the inner pipe 75 and the liquid refrigerant 82 passing through inside the outer pipe 91, and warmed (heated) liquid refrigerant 82 is supplied to the interior heat exchanger 30. The outer pipe 91 also has a function as a receiver with a storage capacity of several hundred cubic centimeters to several liters of refrigerant. When the cooling system 11 is constructed, after the pipes 71 to 75 have been connected, it is possible to fill the pipes 71 to 75 with refrigerant that is held in advance in the outer pipe 91 of the internal heat exchanger 90. The internal heat exchanger 90 is installed in the housing 39 with interior heat exchanger 30. It is possible to dispose the internal heat exchanger (the third heat exchanger) separately from the interior heat exchanger 30, or with the exterior heat exchanger 40.

The changeover valve system 76 is used to switch between the first supply pipe 71 and the second supply pipe 72. The changeover valve system 76 according to the present embodiment includes the first valve CV1 and the second valve CV2. The first valve CV1 is provided at a position midway on the first supply pipe 71, in this case, that is at a position close to the exterior heat exchanger 40-side branching point between the first supply pipe 71 and the second supply pipe 72. The second valve CV2 is provided at a position midway on the second supply pipe 72, in this case, that is close to the exterior heat exchanger 40-side branching point between the first supply pipe 71 and the second supply pipe 72. Note that the changeover valve system 76 only needs to switch between the first supply pipe 71 and the second supply pipe 72 and may be a three-way valve that replaces the two valves CV1 and CV2.

The cooling system 11 further includes temperature sensors TH1 to TH4. The first temperature sensor TH1 is disposed close to an air inlet 38 a of the interior heat exchanger 30 and using the first temperature sensor TH1, it is possible to detect the room temperature of the server room 1. The second temperature sensor TH2 is disposed close to an air outlet 38 b of the interior heat exchanger 30 and using the second temperature sensor TH2, it is possible to detect the temperature of the airflow 65 outputted from the interior heat exchanger 30.

The third temperature sensor TH3 is installed on the outlet pipe 73 of the exterior heat exchanger 40, that is, on the exterior heat exchanger unit 40-side (i.e., upstream) of the branching point between the first supply pipe 71 and the second supply pipe 72. Using the third temperature sensor TH3, it is possible to detect the temperature of the liquid refrigerant outputted from (output of) the exterior heat exchanger 40. The fourth temperature sensor TH4 is disposed on an air intake side of the exterior heat exchanger 40 and using the fourth temperature sensor TH4, it is possible to detect the temperature (outside air temperature) outside the room.

The supplementary cooling system 11 further includes a control unit 50 that controls a fan motor 45 of the interior fan F2 and the changeover valve system 76 (in the present embodiment, the opening and closing of the valves CV1 and CV2). The control unit 50 includes a first functional unit 51, a second functional unit 52, and a third functional unit 53.

The first functional unit 51 includes a function that switches from the second supply pipe 72 to the first supply pipe 71 using the changeover valve system 76 when the temperature of the liquid refrigerant outputted from the exterior heat exchanger 40 (i.e., the temperature detected by the third temperature sensor TH3) becomes equal to or below a first set temperature and if the interior fan F2 has already stopped. In the present embodiment, the first temperature is set as a dew point temperature TD of the server room 1. For example, the humidity inside the server room 1 is controlled using a humidifier or the like so that the dew point is 15° C. or higher according to environmental guidelines intended to prevent static electricity and the like. Accordingly, one example of the dew point temperature TD is 15° C. When the temperature of the liquid refrigerant supplied to the interior heat exchanger 30 is equal to or below the dew point temperature TD, there is the possibility of at least part of the interior tubes 31 of the interior heat exchanger 30 reaching the temperature of the liquid refrigerant, that is, the dew point temperature TD or below, which means there is the possibility of condensation on the surfaces of the interior tubes 31.

In this cooling system 11, the interior heat exchanger 30 does not include an interior fan. Accordingly, the speed of the airflows that pass the interior tubes 31 is not especially high and there is little possibility of water that has condensed on the surfaces of the interior tubes 31 becoming included in the airflow 65. However, when condensation occurs on the interior tubes 31, it is not possible to eradicate the risk of the resulting moisture somehow affecting the servers 5. For this reason, when the temperature of the liquid refrigerant detected by the temperature sensor TH3 is equal to or below the dew point temperature TD, the first supply pipe 71 is selected by the first functional unit 51 and the liquid refrigerant is heated by the vaporized refrigerant using the internal heat exchanger 90. Also, by supplying the liquid refrigerant that has been heated above the dew point temperature TD to the interior heat exchanger 30, the occurrence of condensation on the surfaces of the interior tubes 31 is prevented.

The second functional unit 52 includes a function that stops the exterior fan F2 before the changeover valve system 76 switches from the second supply pipe 72 to the first supply pipe 71 when the temperature of the liquid refrigerant outputted from the exterior heat exchanger 40 is equal to or below the first set temperature (the dew point temperature TD) and if the interior fan F2 has not stopped. By stopping the exterior fan F2, it is possible to lower the heat exchanging efficiency of the exterior heat exchanger 40, which means that there is the possibility of raising the temperature of the liquid refrigerant supplied from the exterior heat exchanger 40. In addition, by stopping the exterior fan F2, it is possible to reduce the power consumption. Accordingly, when the temperature of the liquid refrigerant detected by the temperature sensor TH3 becomes equal to or below the dew point temperature TD, by stopping the exterior fan F2 using the second functional unit 52 before using the first functional unit 51, the occurrence of condensation on the surfaces of the interior tubes 31 is prevented.

When the wind speed outdoors is high and/or the outside temperature is lower, there are cases where the temperature of the liquid refrigerant supplied from the exterior heat exchanger 40 will become equal to or below the dew point temperature TD even if the exterior fan F2 is stopped. In such case, by having the first functional unit 51 operate following the second functional unit 52 to heat the liquid refrigerant in the internal heat exchanger 90, the temperature of the liquid refrigerant supplied to the interior heat exchanger 30 is raised to the dew point temperature TD or higher. Accordingly, with the cooling system 11, it is possible to enable the refrigerant to naturally circulate between the interior heat exchanger 30 and the exterior heat exchanger 40 and to expel the thermal load of the server room 1 outdoors, even under conditions where the temperature of the liquid refrigerant supplied from the exterior heat exchanger 40 is at the dew point temperature TD or below even when the outside fan F2 is stopped.

By bypassing using the second functional unit 52, the first functional unit 51 may switch, by the changeover valve system 76, from the second supply pipe 72 to the first supply pipe 71 without stopping the exterior fan F2 when the temperature of the liquid refrigerant supplied from the exterior heat exchanger 40 becomes equal to or below the first set temperature (the dew point temperature TD). By continuously driving the interior fan F2, both of a drop in the cooling performance and condensation of the interior heat exchanger 30 can be suppressed without lowering the heat exchanging performance of the exterior heat exchanger 40.

The third functional unit 53 includes a function that closes both the first supply pipe 71 and the second supply pipe 72 using the changeover valve system 76 when the outside air temperature detected by the fourth temperature sensor TH4 is equal to or below the second set temperature. If the outside air temperature has fallen excessively and so low as to exceed the performance of the internal heat exchanger 90, there are cases where the temperature of the liquid refrigerant supplied to the interior heat exchanger 30 will be equal to or below the dew point temperature TD even if the interior fan F2 is stopped and the liquid refrigerant is heated in the internal heat exchanger 90. The third functional unit 53 shuts off circulation of the liquid refrigerant between the exterior heat exchanger 40 and the interior heat exchanger 30 in such state to prevent condensation from occurring at the interior heat exchanger 30. The second set temperature is set lower than the first set temperature, and as one example, the second set temperature is set at −20° C.

In this way, in the cooling system 11, in a case (normal state, regular state) where the temperature of the liquid refrigerant outputted from the exterior heat exchanger 40 is above the first set temperature (the dew point temperature TD or above), as shown in FIG. 2, the refrigerant circulates via the second supply pipe 72. That is, the circulation route of the refrigerant is the exterior heat exchanger 40→the supply pipe 73→the second supply pipe 72 (the valve CV2)→the supply pipe 74→the interior heat exchanger 30→the third supply pipe 75→the exterior heat exchanger 40. Note that in the present embodiment, the second supply pipe 72 (the valve CV2) and the supply pipe 74 are in the housing 39 of the interior heat exchanger 30.

On the other hand, when the temperature of the liquid refrigerant outputted from the exterior heat exchanger 40 is equal to or below the first set temperature (dew point temperature TD or above), as shown in FIG. 3, the refrigerant circulates via the first supply pipe 71. That is, the circulation route of the refrigerant is the exterior heat exchanger 40→the supply pipe 73→the first supply pipe 71 (the valve CV1) and the internal heat exchanger 90→the supply pipe 74→the interior heat exchanger 30→the third supply pipe 75→the exterior heat exchanger 40.

In this cooling system 11, the interior tubes 31 of the interior heat exchanger 30 contact a region along the ceiling 3 of the room 1, that is, a high-temperature air zone 63 in the upper part of the room 1, at an angle. When the refrigerant (liquid refrigerant) inside the interior tubes 31 is heated by the high-temperature air zone 63, the refrigerant boils and vaporizes. On the other hand, since the air of the high-temperature air zone 63 loses heat, such air is cooled to produce down flow 65 that flows downward from the region close to the ceiling 3 of the room 1. This flow of air (down flow) 65 flows substantially vertically. Since the interior tubes 31 are disposed so as to be inclined, effective contact is made with the high-temperature air zone 63 that extends in the horizontal direction and the down flow 65 is efficiently produced. Accordingly, it is possible to cool the room 1 comparatively efficiently even when an interior fan is not provided. Note that an interior fan (or “first fan”) may be provided.

In addition, since the interior tubes 31 are inclined with respect to the ceiling 3, the interior tubes 31 draws hot air so as not to interfered with the down flow 65. Accordingly, the air in the high-temperature air zone 63 along the ceiling 3 is efficiently drawn in by the interior heat exchanger 30 to form a certain air flow 64 in the high-temperature air zone 63. This means that according to the cooling system 11, it is possible to eradicate hot spots formed at upper parts of the servers 5 comparatively easily, to promote heat exchanging at the servers 5, and to cool the servers 5 even more effectively.

In this way, with the interior heat exchanger 30, comparatively hot air 64 flows from a nearly horizontal direction substantially across the ceiling 3 into the air intake opening 38 a and cooled air 65 is discharged in a substantially vertical direction from the outtake 38 b. Although the cooling system 11 is capable of cooling the server room 1 on its own, in the example shown in FIG. 1, the cooling system 11 functions as a supplementary air conditioning system for the main air conditioning system 20. The air 65 that has been discharged from the interior heat exchanger 30 of the cooling system 11 is drawn in from the intake 23 a of the floor-standing interior unit 21, is cooled further, and then supplied to the servers 5. Accordingly, under a condition where a cooling effect is manifested by the cooling system 11, the load of the main air conditioning system 20 can be reduced, thereby reducing the power consumption of the main air conditioning system 20. When the interior heat exchanger 30 of the cooling system 11 is used as a supplementary air conditioning system, inside the room it is possible to use an air flow produced by a fan of the main air conditioning system 20. Accordingly, it is possible to omit the interior fan of the cooling system 11.

In addition, in the cooling system 11, since the refrigerant (vaporized refrigerant) that has boiled and vaporized in the interior tubes 31 of the interior heat exchanger 30 circulates in the piping system 70 due to the difference in specific gravity with the liquid refrigerant, a compression device such as a compressor or a pump is not required and aside from fans, fundamentally no power is consumed. Accordingly, it is possible to provide the air conditioning system that has high efficiency and low power consumption. In addition, in the cooling system 11, since the interior tubes 31 are disposed at an angle, air in the room 1 is caused to circulate and to efficiently contact the interior tubes 31. Accordingly, an interior fan does not need to be provided in the interior heat exchanger 30 and the driving force (power) required by such a fan is also unnecessary.

Also, with the cooling system 11, even if the outside air temperature falls and the temperature of the liquid refrigerant supplied from the exterior heat exchanger 40 becomes equal to the dew point or below, by using the internal heat exchanger 90 to heat the liquid refrigerant using the vaporized refrigerant, it is possible to circulate the refrigerant with fundamentally no power consumption and to maintain the cooling performance by natural circulation. Therefore, according to the cooling system 11, it is possible to cool the room 1 with a natural circulation cycle during the night and day and throughout the year, even under conditions where the outside temperature is low, and possible to further reduce the power consumption required by cooling (air conditioning).

FIG. 5 is a flowchart explaining one example of the control method of the cooling system 11. If in step 101 the outside air temperature detected by the temperature sensor TH4 is above −20° C. and in step 102 the temperature of the liquid refrigerant outputted from the exterior heat exchanger 40 (i.e., the temperature detected by the temperature sensor TH3) is greater than the dew point TD, in step 103 the cooling system 11 is driven with the first valve CV1 closed and the second valve CV2 open. By doing so, the refrigerant is circulated in a cycle made up of the exterior heat exchanger 40→the supply pipe 73→the second supply pipe 72 (the valve CV2)→the supply pipe 74→the interior heat exchanger 30→the supply pipe 75→the exterior heat exchanger 40 to cool the room 1 (see FIG. 2). Note that in a condition where the outside temperature is higher than the room temperature and the refrigerant is not condensed in the exterior heat exchanger 40, the refrigerant is not circulated and the room is not cooled using the cooling system 11.

If in step 102 the temperature (temperature sensor TH3) of the liquid refrigerant outputted from the exterior heat exchanger 40 is not greater than the dew point TD, the second function 52 first confirms in step 104 whether the fan F2 is operating and if the fan F2 is operating, stops the fan F2 (the fan motor 45) in step 105. By doing so, it is possible to suppress the heat discharging performance of the exterior heat exchanger 40, which means there is the possibility that the temperature (temperature sensor TH3) of the liquid refrigerant outputted from the exterior heat exchanger 40 will become above the dew point TD. After stopping the fan F2, operation of the cooling system 11 continues in a state where the fan F2 is stopped.

If in step 102 the temperature (temperature sensor TH3) of the liquid refrigerant outputted from the exterior heat exchanger 40 is equal to or below the dew point TD and in step 104 the fan F2 has already stopped, in step 106 the first function 51 opens the first valve CV1 and closes the second valve CV2. By doing so, the refrigerant is circulated in a cycle made up of the exterior heat exchanger 40→the supply pipe 73→the first supply pipe 71 (the valve CV1) and the internal heat exchanger 90→the supply pipe 74→the interior heat exchanger 30→the supply pipe 75→the exterior heat exchanger 40 (see FIG. 3). Note that in this example, the first supply pipe 71 (the valve CV1) and the supply pipe 74 are included in the housing 39 of the interior heat exchanger 30. In this cycle, since the liquid refrigerant is heated by the vaporized refrigerant inside the internal heat exchanger (the third heat exchanger) 90, it is possible to circulate the refrigerant even when the temperature (temperature sensor TH3) of the liquid refrigerant supplied from the exterior heat exchanger 40 becomes equal to or below the dew point TD. Therefore, the amount of circulating refrigerant is maintained) This means that it is possible to move heat inside the room out of the room and continue cooling the room 1 using the natural circulation-type cooling system 11.

If, as described earlier, steps 104 and 105 are omitted and the temperature (temperature sensor TH3) of the liquid refrigerant supplied from the exterior heat exchanger 40 in step 102 is equal to or below the dew point TD, switching of the valves may be carried out by the first functional unit 51 in step 106.

If, in step 101, the outside air temperature detected by the temperature sensor TH4 is equal to or below −20° C., in step 107 the third functional unit 53 closes both the first valve CV1 and the second valve CV2 to stop the circulation of the refrigerant.

FIG. 6 shows an overview of a hybrid air conditioning system 10 b according to another embodiment of the present invention. In the air conditioning system 10 b, the main air conditioning system 20 and the cooling system 11 are disposed in an air conditioning room 7 adjacent to the server room 1, and a partition wall 6 is provided between the server room 1 and the air conditioning room 7. The main air conditioning system 20 takes in air from the server room 1 via an upper opening 6 a of the partition wall 6 and cools such air before expelling the air from an underfloor opening 6 b to an underfloor of the server room 1. Accordingly, the air conditioning room becomes negatively pressured with respect to the server room 1.

The interior heat exchanger 30 of the cooling system 11 that functions as a supplementary system for the main air conditioning system 20 is attached so as to face the upper opening 6 a of the partition wall 6. Accordingly, the interior tubes 31 of the interior heat exchanger 30 are disposed substantially vertically along the partition wall 6. Due to the pressure difference between the server room 1 and the air conditioning room 7, air (warm air) from the server room 1 is supplied to the interior tubes 31, and since the interior tubes 31 extend in the vertical direction, there is high contact efficiency, resulting in the air in the server room 1 being efficiently cooled by the interior tubes 31 and then drawn into the main air conditioning system 20. The exterior heat exchanger 40 of the cooling system 11 is disposed above (i.e., at a higher position than) the interior heat exchanger 30, for example on a deck provided on a higher floor than the floor on which the servers 5 are installed.

In this way, according to the hybrid air conditioning systems 10 a and 10 b that include the cooling system 11 and the control methods thereof, it is possible to operate the natural circulation-type cooling system 11 even if the temperature of the liquid refrigerant supplied from the exterior heat exchanger 40 is equal to or below the dew point, which means that it is possible to carry out cooling with low power consumption over an even longer period. Accordingly, it is possible to provide an air conditioning system with an even lower running cost.

Also, although an example of a cooling system installed in a data center has been described above, the cooling load for the present invention is not limited to information equipment such as servers. The cooling system and hybrid air conditioning system according to the present invention can also be favorably used for cooling in conditions where it is not possible to open a window to let in breezes, such as when cooling a clean room.

In addition, although a cooling system according to the present invention has been described for an example where the system is combined with a floor-standing cooling system, it is also possible to use the system according to the present invention alone or in combination with another type of air conditioning system. Also, aside from being used alone, the cooling system according to the present invention may be used according to a variety of other methods, such as in combination with an existing cooling system, in accordance with the conditions and environment for cooling.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. 

1. A cooling system comprising: a first heat exchanger installed inside a room; a second heat exchanger installed outside the room; and a piping system that enables a refrigerant to naturally circulate between the first heat exchanger and the second heat exchanger, wherein the piping system includes: a first supply pipe that supplies liquid refrigerant from the second heat exchanger to the first heat exchanger, the liquid refrigerant being heated by heat exchanging in a third heat exchanger with vaporized refrigerant supplied from the first heat exchanger to the second heat exchanger; and a second supply pipe that supplies liquid refrigerant from the second heat exchanger to the first heat exchanger bypassing the third heat exchanger.
 2. The cooling system according to claim 1, wherein the piping system further includes a changeover valve system that switches between using the first supply pipe and the second supply pipe, the cooling system further comprises a control unit that controls the changeover valve system, and the control unit includes a functional unit that switches from the second supply pipe to the first supply pipe using the changeover valve system when a temperature of liquid refrigerant outputted from the second heat exchanger becomes equal to or below a first set temperature.
 3. The cooling system according to claim 2, wherein the second heat exchanger includes a second tube and a second fan that supplies outside air to the second tube, wherein the control unit further includes a functional unit that stops the second fan before switching from the second supply pipe to the first supply pipe using the changeover valve system when the temperature of the liquid refrigerant outputted from the second heat exchanger becomes equal to or below the first set temperature.
 4. The cooling system according to claim 2, wherein the control unit includes a functional unit that closes the first supply pipe and the second supply pipe using the changeover valve system when a temperature of outside air becomes equal to or below a second set temperature that is lower than the first set temperature.
 5. A hybrid air conditioning system comprising: a cooling system according to claim 1, and a main air conditioning system that further cools air that has been cooled by the first heat exchanger of the cooling system and supplies cooled air.
 6. A control method of a cooling system, the cooling system including a first heat exchanger installed inside a room, a second heat exchanger installed outside the room, and a piping system that enables a refrigerant to naturally circulate between the first heat exchanger and the second heat exchanger, the piping system including: a first supply pipe that supplies liquid refrigerant, which has been heated by heat exchanging in a third heat exchanger with vaporized refrigerant supplied from the first heat exchanger to the second heat exchanger, from the second heat exchanger to the first heat exchanger; a second supply pipe that supplies liquid refrigerant from the second heat exchanger to the first heat exchanger bypassing the third heat exchanger; and a changeover valve system that switches between using the first supply pipe and the second supply pipe, the control method comprising of switching by a control unit that controls the changeover valve system, from the second supply pipe to the first supply pipe using the changeover valve system when temperature of liquid refrigerant outputted from the second heat exchanger becomes equal to or below a first set temperature.
 7. The control method according to claim 6, wherein the second heat exchanger includes a second tube and a second fan that supplies outside air to the second tube, and the control method further comprises of stopping the second fan before the step of switching when the temperature of the liquid refrigerant outputted from the second heat exchanger becomes equal to or below a first set temperature.
 8. The control method according to claim 6, further comprising closing the first supply pipe and the second supply pipe using the changeover valve system when temperature of outside air becomes equal to or below a second set temperature that is lower than the first set temperature. 